The dynamics of gull-puffin interactions : implications for management
This study investigated the impact of kleptoparasitism and predation by large gulls (Larus spp.) on the recruitment rate, foraging economics and reproductive performance of Atlantic puffins Fratercula arctica breeding on the Isle of May, Firth of Forth, southeast Scotland. The implications of the findings for nature reserve management strategies are discussed. During the period from 1972 to 1989 the population of herring L. argentatus and lesser black-backed gulls L. fuscus nesting on the island was reduced as part of a gull control programme. Since 1989, gull management has involved maintaining gull-free areas by repeated removal of nests. Analysis of data collected over a 23 year period showed that the recruitment rate of puffins to the colony was significantly higher in the areas of the island where gull nest density was low. This suggests that, by reducing the density and spatial distribution of nesting gulls, the control programme successfully increased the attractiveness of the colony as a potential breeding site for puffins. Maintaining gull-free areas was also effective in reducing the frequency with which puffins were attacked by gulls. Kleptoparasitism risk during the morning and evening peaks of puffin feeding activity was 37% in gull-occupied habitat compared to only 5% in gull-free areas. These results indicate that gulls predominantly attacked puffins that bred in close proximity to them and did not move outwith the main gull breeding areas to attack puffins elsewhere on the island. The presence of gulls also significantly reduced the actual rate at which adult puffins attempted to deliver food to their chicks. The lower provisioning rate coupled with the higher kleptoparasitism risk resulted in puffins breeding in gull-occupied habitat delivering 44% fewer food loads to their chicks in the morning and 25% fewer in the evening compared to puffins breeding in gull-free areas. However, despite this difference, there was no evidence of a significant reduction in the growth of puffin chicks or their survival to fledging.